Method for improving expansive soil through urease alkaline residues and construction method of expansive soil

Abstract

The invention relates to the technical field of geotechnical engineering, and provides a method for improving expansive soil through urease alkaline residues and a construction method of the expansive soil. The preparation method comprises the following steps: a, mixing calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, ferric oxide, titanium dioxide and manganese oxide to obtain an alkaline residue mixture; b, carrying out particle screening on the alkaline residue mixture, and reserving alkaline residue particles with the particle size of 0.075-10mm; c, the alkaline residues are pretreated, including water washing, acid pickling and neutralizing treatment, and drying treatment is conducted; and d, mixing the pretreated alkaline residues and expansive soil according to a mass ratio of 5-20% by using mixing equipment, and adjusting the water content to the optimal water content. The alkaline residues are pretreated, including water washing, acid pickling and neutralizing treatment, so that heavy metal impurities and soluble salt in the alkaline residues are effectively removed, the pH value of soil tends to be neutral, the problem of soil acidification or alkalization is avoided, the chemical property of the soil is further improved, and the effect of reducing soil pollution is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, in particular to a method for improving expansive soil with urease alkali residue and a construction method thereof. Background Art

[0002] Expansive soil is a type of soil with special properties. Its main characteristic is that it expands and contracts significantly when the humidity changes. This soil shrinks and cracks when dry, and expands when wet. The main component of expansive soil is montmorillonite clay mineral, which has a strong ability to absorb water and expand. Expansive soil improvement is to reduce its expansion and contraction characteristics, thereby improving its stability and reliability in engineering applications.

[0003] At present, the methods for improving expansive soil mainly include chemical improvement, physical improvement and biological improvement. Among them, the chemical improvement method changes the chemical properties of expansive soil by adding chemical agents such as lime and cement to reduce its expansibility; the physical improvement method improves the physical structure of the soil, such as adding granular materials such as sand and gravel, to improve its stability; the biological improvement method improves the soil structure and reduces expansibility by introducing plant roots. However, these methods have some shortcomings in practical applications.

[0004] Chemical improvement method: Although it can significantly reduce the expansion of expansive soil, it usually requires a large amount of chemical improvers, which is costly and may cause environmental pollution.

[0005] Physical improvement method: requires a large amount of physical materials, and consumes a lot of manpower and material resources during the construction process. The effect is limited by the nature of the materials and the amount added.

[0006] Biological improvement method: The scope of application is small, the effect is limited by environmental conditions, and it is difficult to achieve significant improvement effects in a short period of time. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method for improving expansive soil with urease alkali residue and a construction method thereof, which solves the problem that it is difficult to achieve significant improvement effects in a short period of time and that the environment is polluted during the improvement.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for improving expansive soil with urease alkali residue, comprising the following steps;

[0009] a. mixing calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, iron oxide, titanium dioxide and manganese oxide to obtain an alkali residue mixture;

[0010] b. Screening the alkali residue mixture to retain alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0011] c. Pre-treating the alkali residue, including water washing, acid washing and neutralization, and drying;

[0012] d. Use a mixing device to mix the pretreated alkali residue with expansive soil at a mass ratio of 5% to 20%, and adjust the water content to the optimum water content;

[0013] e. Adding improvers, including one or more of the following ingredients, fly ash, lime, silica fume and urease, and mixing the alkali slag and improvers in a mass ratio of 95%:5% for a second time.

[0014] Preferably, the alkali slag composition ratio in step a includes 30% to 50% calcium oxide, 5% to 10% magnesium oxide, 10% to 20% silicon dioxide, 1% to 5% aluminum oxide, 20% to 40% iron oxide, 0.5% to 2% titanium dioxide and 1% to 5% manganese oxide.

[0015] Preferably, the screening device in step b is a vibrating screen, and the screen hole size is set to 0.075 mm to 10 mm.

[0016] Preferably, the pretreatment in step c comprises the following steps:

[0017] c. 1. Put the alkali residue particles into the cleaning tank and wash them with circulating water for 20min to 30min to remove harmful impurities from Kexing;

[0018] c. 2. Wash the alkali residue in dilute hydrochloric acid for 15 to 20 minutes. The concentration of dilute hydrochloric acid is controlled at 5% to 12% to remove heavy metal impurities. After pickling, neutralize the residue to ensure that the pH value is between 5 and 9.

[0019] c, 3. Dry the pretreated alkali residue at a temperature of 60°C to 100°C.

[0020] Preferably, the mixing equipment in step d is a spiral stirrer to evenly mix the alkali residue and the expansive soil, and the mixing time is 10 min to 25 min.

[0021] Preferably, the water content in step d is controlled at 10% to 15%.

[0022] Preferably, a construction method for improving expansive soil with urease alkali residue comprises the following steps:

[0023] Step 1: Use a vibrating screening device to grade and screen the alkali residue, set the sieve size of the screening device to 0.075 mm to 10 mm, so as to ensure that particles with a particle size exceeding 10 mm are screened out, and the alkali residue particles with a particle size between 0.075 mm and 10 mm are retained, and the screened alkali residue particles are collected;

[0024] Step 2: Put the sieved alkali residue particles into a cleaning tank, wash them with circulating water for 20 minutes to 30 minutes to remove soluble harmful impurities, use dilute hydrochloric acid to pickle the alkali residue particles for 15 minutes to 20 minutes, and control the concentration at 5% to 12% to remove heavy metal impurities. After pickling, neutralize them to ensure that the pH value of the alkali residue is between 5 and 9 to avoid secondary pollution to the soil and the environment. Dry the pretreated alkali residue at a drying temperature of 60°C to 100°C to prevent chemical changes in the alkali residue particles.

[0025] Step 3: Use a spiral stirrer to evenly mix the pretreated alkali residue and expansive soil in a determined ratio, and the mixing time is 10 minutes to 25 minutes. During the mixing process, add water in an appropriate amount according to the optimum moisture content of the soil, and control the moisture content at 10% to 15% to ensure that the moisture of the mixture reaches the optimal state. Add improvers, including fly ash, lime, silica fume and urease, and perform secondary mixing at a mass ratio of alkali residue to improver of 95%:5%. The mixing time is 10 minutes to 25 minutes to ensure that the improver is evenly distributed in the mixture;

[0026] Step 4: After the site is cleaned, lay the evenly mixed alkali slag expansive soil mixture in layers, with the thickness of each layer controlled at 15mm to 20mm. Use a vibrating roller to compact each layer, treat the surface of the improved expansive soil, and spray a curing agent to form a protective layer to reduce surface weathering and erosion.

[0027] The present invention provides a method for improving expansive soil by urease alkali residue and a construction method thereof.

[0028] Beneficial effects:

[0029] 1. The present invention pre-treats the alkali residue, including water washing, acid washing and neutralization treatment, to effectively remove heavy metal impurities and soluble salts in the alkali residue, and makes the pH value of the soil tend to be neutral to avoid the problem of soil acidification or alkalinization, further improve the chemical properties of the soil, and achieve the effect of reducing soil pollution.

[0030] 2. The present invention generates hydrated calcium silicate and hydrated calcium aluminate by reacting calcium oxide in the alkali residue with silicate and aluminate in the expansive soil. These products fill the gaps between soil particles to form a stable soil structure, thereby enhancing the strength and stability of the soil. Calcium ions and magnesium ions in the alkali residue undergo ion exchange reaction with sodium ions in the expansive soil, thereby reducing the sodium ion concentration in the expansive soil and thus reducing the expansion potential of the soil.

[0031] 3. The present invention adds a modifier, and the active ingredients in the fly ash react chemically with the ingredients in the alkali slag to generate cementing substances such as hydrated calcium silicate, thereby enhancing the strength and stability of the soil. Lime can significantly improve the unconfined compressive strength of the soil, so that the improved expansive soil has a better bearing capacity. The active silicon dioxide in the silica ash can react with the calcium compounds in the alkali slag to generate more hydrated calcium silicate, thereby enhancing the structural stability and compressive strength of the soil. The active ingredients in the mineral powder can react with the ingredients in the alkali slag and the expansive soil to generate cementing compounds, thereby improving the strength and durability of the soil. Urease can induce calcium carbonate precipitation by inducing microorganisms. Urease catalyzes the decomposition of urea to generate bicarbonate and ammonia. After the bicarbonate reacts with calcium ions in the environment, it forms calcium carbonate precipitation, which can fill the pores between soil particles, thereby improving the strength and stability of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example:

[0035] Please see attached Figure 1 , an embodiment of the present invention provides a method for improving expansive soil by using urease alkali residue, comprising the following steps;

[0036] a. mixing calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, iron oxide, titanium dioxide and manganese oxide to obtain an alkali residue mixture;

[0037] b. Screening the alkali residue mixture to retain alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0038] c. Pre-treating the alkali residue, including water washing, acid washing and neutralization, and drying;

[0039] d. Use a mixing device to mix the pretreated alkali residue with expansive soil at a mass ratio of 5% to 20%, and adjust the water content to the optimum water content;

[0040] e. Adding improvers, including one or more of the following ingredients, fly ash, lime, silica fume and urease, and mixing the alkali slag and improvers in a mass ratio of 95%:5% for a second time.

[0041] The alkali slag composition ratios in step a include 30% to 50% calcium oxide, 5% to 10% magnesium oxide, 10% to 20% silicon dioxide, 1% to 5% aluminum oxide, 20% to 40% iron oxide, 0.5% to 2% titanium dioxide and 1% to 5% manganese oxide.

[0042] In the step b, the screening device is a vibrating screen, and the screen hole size is set to 0.075 mm to 10 mm.

[0043] The pretreatment in step c comprises the following steps:

[0044] c. 1. Put the alkali residue particles into the cleaning tank and wash them with circulating water for 20min to 30min to remove harmful impurities from Kexing;

[0045] c. 2. Wash the alkali residue in dilute hydrochloric acid for 15 to 20 minutes. The concentration of dilute hydrochloric acid is controlled at 5% to 12% to remove heavy metal impurities. After pickling, neutralize the residue to ensure that the pH value is between 5 and 9.

[0046] c, 3. Dry the pretreated alkali residue at a temperature of 60°C to 100°C.

[0047] The mixing device in step d is a spiral stirrer to evenly mix the alkali residue and the expansive soil, and the mixing time is 10 minutes to 25 minutes.

[0048] In the step d, the water content is controlled at 10% to 15%.

[0049] Embodiment 1;

[0050] Alkali residue ratio (by weight percentage):

[0051] Calcium oxide (CaO): 40%

[0052] Magnesium oxide (MgO): 7%

[0053] Silicon dioxide (SiO2): 15%

[0054] Alumina (Al2O3): 3%

[0055] Iron oxide (FeO, Fe2O3): 30%

[0056] Titanium dioxide (TiO2): 1%

[0057] Manganese oxide (MnO): 4%

[0058] Implementation steps;

[0059] Use vibration screening equipment to grade and screen the alkali residue, and retain the alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0060] Put the sieved alkali residue particles into a cleaning tank, wash them with circulating water for 30 minutes, then wash them with 10% dilute hydrochloric acid for 20 minutes, and neutralize them to ensure that the pH value of the alkali residue is 7;

[0061] The pretreated alkali residue is dried, and the drying temperature is controlled at 80°C;

[0062] The pretreated alkali residue and expansive soil were mixed at a mass ratio of 15% using a spiral stirrer for 20 minutes, and the water content was adjusted to 12%;

[0063] Add fly ash as a modifier, mix them in a mass ratio of 95%:5% of alkali slag and modifier, and mix them for 10 minutes;

[0064] Summary of Embodiment 1;

[0065] By using fly ash as a modifier through the above steps, the expansion rate was significantly reduced to 3%, the unconfined compressive strength was increased to 300 kPa, and the density was increased to 1.85 g / cm 3 , the moisture content is 12%, the improvement effect is significant, and the engineering properties of the soil are improved.

[0066] Embodiment 2:

[0067] Alkali residue ratio (by weight percentage):

[0068] Calcium oxide (CaO): 35%

[0069] Magnesium oxide (MgO): 8%

[0070] Silicon dioxide (SiO2): 18%

[0071] Alumina (Al2O3): 2%

[0072] Iron oxide (FeO, Fe2O3): 32%

[0073] Titanium dioxide (TiO2): 1%

[0074] Manganese oxide (MnO): 4%

[0075] Implementation steps;

[0076] Use vibration screening equipment to grade and screen the alkali residue, and retain the alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0077] Put the sieved alkali residue particles into a cleaning tank, wash them with circulating water for 25 minutes, then wash them with 8% dilute hydrochloric acid for 18 minutes, and neutralize them to ensure that the pH value of the alkali residue is 6.5;

[0078] The pretreated alkali residue is dried, and the drying temperature is controlled at 70°C;

[0079] The pretreated alkali residue and expansive soil were mixed at a mass ratio of 10% using a spiral stirrer for 15 minutes, and the water content was adjusted to 11%;

[0080] Add lime as an improver, mix the alkali residue and improver in a mass ratio of 95%:5%, and mix for 10 minutes;

[0081] Summary of Embodiment 2;

[0082] By using lime as a modifier through the above steps, the expansion rate is reduced to 4%, the unconfined compressive strength is increased to 290 kPa, and the density is increased to 1.80 g / cm 3 , with a water content of 10%. Lime effectively enhances the stability and strength of the soil.

[0083] Embodiment three;

[0084] Alkali residue ratio (by weight percentage):

[0085] Calcium oxide (CaO): 38%

[0086] Magnesium oxide (MgO): 6%

[0087] Silicon dioxide (SiO2): 17%

[0088] Alumina (Al2O3): 3%

[0089] Iron oxide (FeO, Fe2O3): 29%

[0090] Titanium dioxide (TiO2): 1.5%

[0091] Manganese oxide (MnO): 2.5%

[0092] Implementation steps:

[0093] Use vibration screening equipment to grade and screen the alkali residue, and retain the alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0094] Put the sieved alkali residue particles into the cleaning tank, wash them with circulating water for 20 minutes, then wash them with 6% dilute hydrochloric acid for 15 minutes, and neutralize them to ensure that the pH value of the alkali residue is 7;

[0095] The pre-treated alkali residue is dried, and the drying temperature is controlled at 90°C;

[0096] The pretreated alkali residue and expansive soil were mixed at a mass ratio of 20% using a spiral stirrer for 25 minutes, and the water content was adjusted to 13%;

[0097] Add silica fume as a modifier, mix the alkali slag and the modifier in a mass ratio of 95%:5%, and mix for 10 minutes;

[0098] Summary of Example 3;

[0099] By using silica fume as a modifier through the above steps, the expansion rate is reduced to 3.5%, the unconfined compressive strength is increased to 310 kPa, and the density is increased to 1.82 g / cm 3 , with a water content of 11%. Silica fume significantly improves the engineering properties of soil.

[0100] Embodiment 4:

[0101] Alkali residue ratio (by weight percentage):

[0102] Calcium oxide (CaO): 37%

[0103] Magnesium oxide (MgO): 7%

[0104] Silicon dioxide (SiO2): 16%

[0105] Alumina (Al2O3): 2.5%

[0106] Iron oxide (FeO, Fe2O3): 31%

[0107] Titanium dioxide (TiO2): 1.2%

[0108] Manganese oxide (MnO): 3%

[0109] Implementation steps:

[0110] Use vibration screening equipment to grade and screen the alkali residue, and retain the alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0111] Put the sieved alkali residue particles into the cleaning tank, wash them with circulating water for 28 minutes, wash them with 7% dilute hydrochloric acid for 20 minutes, and neutralize them to ensure that the pH value is 6.8;

[0112] The pretreated alkali residue is dried, and the drying temperature is controlled at 85°C;

[0113] The pretreated alkali residue and expansive soil were mixed at a mass ratio of 12% using a spiral stirrer for 25 minutes, and the water content was adjusted to 12%;

[0114] Urease was added as an improver, and the alkali residue and the improver were mixed in a mass ratio of 95%:5% for 10 minutes;

[0115] Summary of Embodiment 4:

[0116] Through the above steps, urease was used as a modifier, and the expansion rate was reduced to 2.5%, the unconfined compressive strength was increased to 320 kPa, and the density was increased to 1.80 g / cm 3 , the water content is 11%. Urease effectively enhances soil stability by inducing calcium carbonate precipitation through microorganisms, making the improvement effect of expansive soil more significant.

[0117] Embodiment five;

[0118] Alkali residue ratio (by weight percentage):

[0119] Calcium oxide (CaO): 36%

[0120] Magnesium oxide (MgO): 7.5%

[0121] Silicon dioxide (SiO2): 17%

[0122] Alumina (Al2O3): 3.5%

[0123] Iron oxide (FeO, Fe2O3): 28%

[0124] Titanium dioxide (TiO2): 1%

[0125] Manganese oxide (MnO): 3%

[0126] Implementation steps:

[0127] Use vibration screening equipment to grade and screen the alkali residue, and retain the alkali residue particles with a particle size between 0.075 mm and 10 mm;

[0128] Put the sieved alkali residue particles into the cleaning tank, wash them with circulating water for 25 minutes, then wash them with 9% dilute hydrochloric acid for 18 minutes, and neutralize them to ensure that the pH value of the alkali residue is 6.5;

[0129] The pretreated alkali residue is dried, and the drying temperature is controlled at 80°C;

[0130] The pretreated alkali residue and expansive soil were mixed at a mass ratio of 18% using a spiral stirrer for 22 minutes, and the water content was adjusted to 14%;

[0131] Add fly ash and urease as improvers, mix them in a mass ratio of 95%:5% of alkali residue and improver, and mix them for 12 minutes;

[0132] Summary of Embodiment 5;

[0133] By using fly ash and urease as modifiers in the above steps, the expansion rate was reduced to 3%, the unconfined compressive strength was increased to 315 kPa, and the density was increased to 1.83 g / cm 3 , the water content is 12%. The addition of urease further enhances the consolidation effect of alkali slag expansive soil, making the soil more stable in the change of water content.

[0134] Experimental design;

[0135] Purpose:

[0136] The effects of different improvers on alkali slag improved expansive soil were verified, and the changes in expansion rate, unconfined compressive strength, density and water content of the expansive soil before and after improvement were compared.

[0137] Experimental steps:

[0138] Materials preparation:

[0139] Traditional preparation method: expansive soil and alkali slag.

[0140] Embodiments of the present invention: expansive soil, alkali slag mixture and improvers (fly ash, lime, silica fume and urease).

[0141] Material ratio:

[0142] Materials were prepared in the weight percentages specified in the respective Examples and Conventional Methods.

[0143] Mixing and stirring:

[0144] Traditional method: Use ordinary mixing equipment to mix and ensure uniformity.

[0145] The method of the invention comprises the following steps: using a vibration screening device to screen the alkali residue mixture, then washing, acid washing, neutralizing and drying the mixture, using a spiral stirrer to mix the alkali residue mixture with expansive soil, and adding an improver during the mixing process for secondary mixing.

[0146] Test items:

[0147] Expansion rate

[0148] Unconfined compressive strength

[0149] density

[0150] Water content

[0151] Table 1:

[0152]

[0153] Summarize:

[0154] By comparing the traditional improved method and the five embodiments of the present invention, the performance of different methods in terms of expansion rate, unconfined compressive strength, density and water content is comprehensively evaluated. The experimental data are shown in Table 1, and the specific analysis is as follows;

[0155] Expansion rate;

[0156] Traditional improvement method: The expansion rate is 12%, which shows the high expansion property of expansive soil.

[0157] In the embodiment of the present invention, the expansion rates of all experimental groups were significantly reduced, especially in experimental group 1 and experimental group 3, where the expansion rates were reduced to 3% and 3.5%, respectively, indicating that the improvement effect was significant.

[0158] Unconfined compressive strength;

[0159] Traditional improvement method: The compressive strength is 150 kPa. The lower compressive strength shows the weak bearing capacity of the unimproved soil.

[0160] Embodiment of the present invention: The compressive strength of all experimental groups was significantly improved, and the compressive strength of experimental group 4 reached 320 kPa, indicating that urease induced calcium carbonate precipitation through microorganisms, thereby greatly improving soil strength.

[0161] density;

[0162] Traditional improved method: density is 1.75g / cm 3 .

[0163] Embodiment of the present invention: The density of all experimental groups is higher than that of the traditional improved method. The density of experimental group 5 combining urease and fly ash is the highest, reaching 1.83g / cm 3 , indicating that urease acted synergistically with other amendments to enhance soil compaction.

[0164] Water content;

[0165] Traditional improved method: moisture content is 11%.

[0166] Embodiment of the present invention: The water content of each experimental group did not change much, all between 10% and 12%, indicating that the improved soil performed consistently in maintaining water content.

[0167] Heavy metal content:

[0168] Traditional improvement method: The heavy metal content was 50 mg / kg, indicating a high level of heavy metal pollution.

[0169] Embodiment of the present invention: The heavy metal contents of all experimental groups were significantly lower than those of the traditional improvement method, and the heavy metal contents were reduced to 10 mg / kg and 11 mg / kg, respectively, indicating that the heavy metal pollution in the soil was effectively reduced through pretreatment.

[0170] pH value:

[0171] Traditional Amendment Method: The pH value is 8.5, indicating possible alkalinity problems in the soil.

[0172] Embodiment of the present invention: The method of the present invention makes the soil pH value tend to be neutral, and the pH value of experimental group 1 and experimental group 3 is 7.0, avoiding the problem of soil acidification or alkalinization.

[0173] Soluble salt content:

[0174] Traditional improvement method: the soluble salt content is 1.2%.

[0175] In the present invention, the soluble salt content of all experimental groups was lower than that of the traditional improvement method, and the soluble salt content was reduced to 0.4% and 0.5%, respectively, indicating that the improvement of soil is effective in reducing salt accumulation.

[0176] Summarize and summarize;

[0177] The experimental results clearly show that the method of the present invention is superior to the traditional method in various performance indicators, specifically:

[0178] The expansion rate was significantly reduced

[0179] The unconfined compressive strength is significantly improved, which significantly improves the strength and bearing capacity of the soil

[0180] Significantly higher density, improving soil compaction and making it more stable

[0181] The performance in terms of water content is consistent;

[0182] The heavy metal content was significantly reduced, effectively reducing the heavy metal pollution in the soil;

[0183] The pH value tends to be neutral, avoiding the soil acidification or alkalinization problems that may be caused by traditional methods;

[0184] The soluble salt content was significantly reduced, effectively reducing the salt accumulation in the soil.

[0185] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving expansive soil by using urease alkali residue, characterized in that: The steps include: a. mixing calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, iron oxide, titanium dioxide and manganese oxide to obtain an alkali residue mixture; b. Screening the alkali residue mixture to retain alkali residue particles with a particle size between 0.075 mm and 10 mm; c. Pre-treating the alkali residue, including water washing, acid washing and neutralization, and drying; d. Use a mixing device to mix the pretreated alkali residue with expansive soil at a mass ratio of 5% to 20%, and adjust the water content to the optimum water content; e. Adding improvers, including one or more of the following ingredients, fly ash, lime, silica fume and urease, and mixing the alkali slag and improvers in a mass ratio of 95%:5% for a second time.

2. The method for improving expansive soil with urease alkali residue according to claim 1, characterized in that: The alkali slag composition ratios in step a include 30%-50% calcium oxide, 5%-10% magnesium oxide, 10%-20% silicon dioxide, 1%-5% aluminum oxide, 20%-40% iron oxide, 0.5%-2% titanium dioxide and 1%-5% manganese oxide.

3. The method for improving expansive soil with urease alkali residue according to claim 1, characterized in that: In the step b, the screening device is a vibrating screen, and the screen hole size is set to 0.075 mm to 10 mm.

4. The method for improving expansive soil with urease alkali residue according to claim 1, characterized in that: The pretreatment in step c comprises the following steps: c.

1. Put the alkali residue particles into the cleaning tank and wash them with circulating water for 20min to 30min to remove harmful impurities from Kexing; c.

2. Wash the alkali residue in dilute hydrochloric acid for 15 to 20 minutes. The concentration of dilute hydrochloric acid is controlled at 5% to 12% to remove heavy metal impurities. After pickling, neutralize the residue to ensure that the pH value is between 5 and 9. c, 3. Dry the pretreated alkali residue at a temperature of 60°C to 100°C.

5. The method for improving expansive soil with urease alkali residue according to claim 1, characterized in that: The mixing device in step d is a spiral stirrer to evenly mix the alkali residue and the expansive soil, and the mixing time is 10 minutes to 25 minutes.

6. The method for improving expansive soil with urease alkali residue according to claim 1, characterized in that: In the step d, the water content is controlled at 10% to 15%.

7. A construction method for improving expansive soil with urease alkali residue, characterized in that: The method for improving expansive soil using the urease alkali residue described in any one of claims 1 to 8 comprises the following steps: Step 1: Use a vibrating screening device to grade and screen the alkali residue, set the sieve size of the screening device to 0.075 mm to 10 mm, so as to ensure that particles with a particle size exceeding 10 mm are screened out, and the alkali residue particles with a particle size between 0.075 mm and 10 mm are retained, and the screened alkali residue particles are collected; Step 2: Put the sieved alkali residue particles into a cleaning tank, wash them with circulating water for 20 minutes to 30 minutes to remove soluble harmful impurities, use dilute hydrochloric acid to pickle the alkali residue particles for 15 minutes to 20 minutes, and control the concentration at 5% to 12% to remove heavy metal impurities. After pickling, neutralize them to ensure that the pH value of the alkali residue is between 5 and 9 to avoid secondary pollution to the soil and the environment. Dry the pretreated alkali residue at a drying temperature of 60°C to 100°C to prevent chemical changes in the alkali residue particles. Step 3: Use a spiral stirrer to evenly mix the pretreated alkali residue and expansive soil in a determined ratio, and the mixing time is 10 minutes to 25 minutes. During the mixing process, add water in an appropriate amount according to the optimum moisture content of the soil, and control the moisture content at 10% to 15% to ensure that the moisture of the mixture reaches the optimal state. Add improvers, including fly ash, lime, silica fume and urease, and perform secondary mixing at a mass ratio of alkali residue to improver of 95%:5%. The mixing time is 10 minutes to 25 minutes to ensure that the improver is evenly distributed in the mixture; Step 4: After the site is cleaned, lay the evenly mixed alkali slag expansive soil mixture in layers, with the thickness of each layer controlled at 15mm to 20mm. Use a vibrating roller to compact each layer, treat the surface of the improved expansive soil, and spray a curing agent to form a protective layer to reduce surface weathering and erosion.

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